Amplifying system for vacuum-tube circuits



Dec. 14 1926. 1,610,918

, E. G. BEARD AMPLIFYING SYSTEM FOR VACUUM TUBE CIRCUITS Filed April 22, 1926 2 SheetsShee+ 1 I ,6. Zwcnfor:

[nest GBea d E. G. BEARD AMPLIFYING SYSTEM FOR VACUUM TUBE CIRCUITS Dec. 14, 1926.

Filed April 22, 1926 2 Sheets-Sheet 2 Patented Dec. 14, 1926.

UNITED STATES PATENT OFFICE.

ERNEST GORDON BEARD, OF NORTH SYDNEY. NEW SOUTH \VALES, AUSTRALIA, AS- SIGNOR TO UNITED DISTRIBUTORS LIMITED, OF SYDNEY, AUSTRALIA.

AMPLIFYING SYSTEM FOR VACUUM-TUBE CIRCUITS.

Application filed April 22,1926, Serial No. 103,910, and in Australia November 20, 1924.

This invention relates to improvements in cascade amplification systems for use with radio receiving and transmitting apparatus, wired wireless systems, carrier-wave telegraphy and telephony and the like.

The invention is particularly applicable to radio receiving systems, and it provides a method or system of coupling thermionic amplifying valves in cascade whereby eflicient amplification either at radio-frequency or audio-frequency can be obtained over a large band of frequencies. The invention also provides a system of cascade amplification which is suitable for convenient manufacture and can be easily manipulated and controlled even by inexperienced operators.

It is recognized that when thermionic valves are coupled together in cascade for amplification, the most eflicient results are obtained when the following four requirements are satisfied 1. The impedance of the plate circuit of an amplifying valve should equal the internal impedance of the valve.

2. The impedance in the coupling circuit between the plate of one amplifying valve and the grid of thefollowing amplifying valve should be as low as possible.

3. The damping of any valve coupling system due to the plate of the preceding valve should be equalized by the damping of the grid of the followin valve.

4. The path from the grid to the plate of a valve should possess infinite impedance, or, alternatively, it should be so balanced by a path. for currents or impulses of opposite phase that its effect in no way differs from that of an infinite impedance.

When the fourth requirement is not satisfied the stability of the amplifying system depends on the characteristics of the plate circuit impedance and is effected in the following three ways (a) If the plate circuit impedance be inductive, the effective resistance of the grid circuit is lowered and the amplifying system is'rendered unstable.

(6) If the plate circuit impedance be capacitive, the resistance of the grid circuit is increased and the amplifying system is rendered stable. v (a) If the plate circuit impedance be re; sistive only, no effect on the grid circuit will exist due to the self-capacity of the valve between the grid and the plate.

In an endeavor to satisfy the four above set-out requirements, several systems have previously been adopted or proposed, including:

(a) The use of aperiodic transformers.

This system, in use, is not very satisfac-- with this system by using a neutralizing circuit on the Hazeltine neutrodyne system, but this addition makes the system very difficult to control. (0) The use of tuned plate circuits.

This system satisfies requirements numbered 1 and 2 but it does not meet the re-v quirements numbered 3 or 4:.

(d) The use of resistance capacity couplings between the valves.

This system gives good results at low fre-. quency, but at high frequency the results are very unsatisfactory due to the fact that the impedances of the various self-capacities in the plate and grid circuits become considerably less than the impedances of the couplin resistances or chokes. The present invention relates particularly to improvements in the resistance capacity system of coupling valves for cascade amplification, and its principal object is to remove the limitation above-mentioned, thus enabling efficient amplification results to be obtained at high frequency.

The invention consists essentially in combining inductances with the self-capacities in the plate and grid circuits of the valves in such a manner as to increase the impedance of the coupling system until it is been successfully used,.

tance produces in the late circuit of the valve a resistive impe ance which can be made to equal the internal impedance of the valve by adjusting the size of the plate resistance or' choke.

Reference is now made to the accompany .across the coupling resistance or choke.

Figure 4 illustrates a form of the invention wherein a resistance or choke is inserted in series with the coupling condenser:

Figure 5 is a View of an alternative form of the invention.

Figure 6 is a diagrammatic view of the coupling between two valves showing one method of balancing-out self capacity between the grid and plate of the following valve.

Figures 7, 8 and 9 are similar views illustrating other methods of balancing-out self capacity between the grid and plate of the following valve.

Referring initially to Figure 1 of these diagrammatic views, 1 indicates the aerial of a radio receiving system, 2 the aerial circuit, 3, 4 and 5 the thermionic valves, '6 the low-tension battery for supplying current to the valve filaments, 7 the filament circuits; 8 the high-tension battery for the valve plates, and 9the head-phones. The valves are coupled together in cascade by couplings of the resistance capacity type, comprising resistances or chokes 10 and fixed condensers 11.

Accordin to the invention the impedance of each vafile coupling is increased by inserting an inductance 12-between the grid and the filament of the following valve. This inductance produces in the plate circuit of the valve a resistive impedance which can be made to equal the internal impedance of the valve, 'so as to satisfy the requirement No. 1 above, by adjusting the size of the plate resistance or choke 10. If desired, a variable cpndenser such as 13 may be shunted across each of the inductances 12. The. etiiciency of the valve coupling system can be improved by satisfying requirement No. 3 above in any one of the following three ways 1. By using a variable coupling condenser 14 in lieu of the fixed coupling-condenser 11 and by varying the capacity of this condenser until the required damping condition is obtained-see Figure 2.

2. By connecting capacity such as the variable condenser 15, across the coupling resistance or choke 10 and by varying this capacity until the required damping condition is obtained-see Figure 3.

3. By inserting a resistance or choke 16 in series with the coupling capacity 11--see Figure 4. This resistance or choke may have a shunting condenser. such as 17.

By any one of theabove three methods the damping of the coupling system due to the preceding valve or aerial is equalized by the damping due to the following valve. Furthermore, the impedance of the valve can be equalized by the impedance of the plate circuit, which being either resistive or capacitive will thus give required stability to the circuit.

It is recognized that when cascade coupled valves are naturally regenerative, stability can be efiiciently obtained by increasing the current transformation ratio between the valves until the resistance losses are increased to the required degree. Thus, to obtain stability in any of the systems above described, the variable condensers 14 or 15 or the resistance 16 may be so varied as to increase the current transformation ratio between the plate of one valve and the grid of the following valve to increase the power loss as desired.

In an alternative form of the invention illustrated by Figure 5, the requirement No. 3 above'is satisfied by connecting a condenser 18 of suitable value across the plate res'stance or choke 10 and by inserting a tuning unit 19 in series between the plate and filament or the coupled valves. This tuning unit ('onsists of a variable condenser 20 and an inductance 21. and the grid of the following valve is connected to the high potential end of the said inductance. in this form of the invention the required damping condition is obtained by adjusting the condenser 18 which is connected across the coupling resistance or choke It). To obtain required stability, the condenser 18 maybe varied until the current transformation ratio is of such value that natural regeneration is unable to overcome the resistance losses and still maintain which may be shunted by a capacity 24..

The necessary equalization of damping due to the two valves may in this form of the invcntion be achieved by (a) Connecting a. variable condenser 25 between the grid and the filament of the fol- Figure 7, or

() Connecting a capacity 27 across the coupling resistance or choke and also by connecting a capacity 28 between the grid and the filament of the following valve, and then adjusting these two capacities as necessarysee Figure 8.

lVith any of these three systems the effect of the self-capacity between. the grid and the plate of the following valve may be balanced-out by introducing extra condensers 29 between the extremities of the inductances 23 and the plate of the following valve, and by adjusting these condensers un til the valve 'plate is at the same high-frequency potential with respect to the extremities of the inductance as is the filament of the valve. 7 I

Although the theory under which this circuit operates to produce the neutralization has not been fully established, it is believed that the neutralization eilect is probably produced as follows:' The tube 4 (Fig. 7) has parasitic oscillations of much higher frequency than the broadcasting frequency and, if the circuit.

\ including the impedance 23 and fixed confinite impedance.

denser 2a is in tune with this parasitic fre quency it will virtually constitute an in- A Under these circumstances the circuit at opposite ends of the impedance 23 will be of opposite polarity and conseuently the signal fed back from the plate to t 1e rid of tube 4 and through the variable con enseror capacity 29 will reach the end of impedance 23 next the tube 3 in opposite polarity to the signal passing from the plate of tube 4 to the same point. Thus by adjusting the variable condenser 29 the two signals of opposite polarity may be made ofvalve by means of a condenser 32 of suitable size, and balancing condensers 33 and 34 are connected across the extremities of said coupling condenser 32. This system is much simpler to control than the well-known neutrodyne system wherein the grid is balanced in relation to the plate. In lieu of the balancing condensers 33 and 34, inductances of suitable value may be employed if so desired.

The valve coupling systems herein described may be. readily applied to coupling an aerial to the grid of the first Valve of a wireless rceiver in order to equalize the radiation damping of the aerial with the damping due to the first valve of the re celver. necting the aerial l to the grid of the first valve by means of an inductance 35 and a capacity 36 in parallel-see Figure 8; A condenser 37 is connected between the grid and the filament of the valve, and balancing condensers 38 and 39 are connected from the plate of the valve to the extremities of the inductance 35. In this form of coupling the filament is earthed and the damping due to the grid of the valve is varied as required by adjusting the condenser 37 'VVhen using any of the coupling systems or methods embodied in the invention, the selectivity of the couplings may be increased to any desired degree by so adjusting the circuits that the damping due to the preceding valve or aerial is reduced below that requisite for maximum efficiency.

To simplify the control and the operation of wireless receivers using the improved couplings, the inter-valve coupling capacities may be first switched into use when the additional circuits embodied in the invention are successively brought into use in-any sequence.

What ll do claim is y.

In an amplifying system for vacuum tube circuits, a plurality of vacuum tube amplifiers arranged in cascade, a circuit connection between the late of one tube and the grid of the following tube, a capacity in said connection, an inductance in said circuit in series with said capacity, a capacity in shunt with the inductance, and balancing capaci' ties connected between the extremities of said inductance and the plate of the following tube.

In testimony whereof I affix my signature.

eonnon nnann.

This may be accomplished by conlltl 

